后循环缺血患者椎基底动脉狭窄的3D-TOP-MRA与DSA对照研究

目的:对照分析后循环缺血患者椎基底动脉的3D-TOP-MRA和DSA检查结果,探讨3D-TOP-MRA用于后循环缺血的诊断价值。方法:选取80例后循环缺血患者分别完成椎基底动脉的3D-TOP-MRA和DSA检查,以盲法判断动脉血管的狭窄情况,对比分析两种方法检测结果间的相关性,并系统评价3D-TOP-MRA的诊断效率。结果:以DSA为金标准,3D-TOP-MRA检测出狭窄血管的总体灵敏度为88.23%,轻度、中度、重度狭窄和闭塞的灵敏度分别为57.89%、96.30%、85.71%和100%。3D-TOP-MRA检查出狭窄血管总体特异度为66.67%,轻度、中度、重度狭窄和闭塞的特异度分别为100%、96.23%、92.42%和100%。3D-TOP-MRA检查出狭窄血管的总体准确度为85.00%,轻度、中度、重度狭窄和闭塞的准确度分别为90.00%、96.25%、91.25%和100%。结论:3D-TOP-MRA无创检测后循环缺血患者椎基底动脉的狭窄有较高的准确度和灵敏度,特别是中重度狭窄病例,可作为血管狭窄术前筛查、术后随访重要检查手段,有利于控制后循环缺血诊治过程中的临床风险。      

Directional site effects in a non-volcanic gas emission area (Mefite d’Ansanto,southern Italy): Evidence of a local transfer fault transversal to large NW–SE extensional faults?

The technique of the wavefield polarization is applied to ambient vibrations recorded in the Mefite d’Ansanto area, an important non-volcanic natural emission of low temperature CO₂ enriched gases. Twenty-five measurements were performed in the study area, eleven near the emission site and the other fourteen in different sites within an area of 5 km. Polarization is assessed both in the frequency and time domain through the individual-station horizontal-to-vertical spectral ratio and covariance-matrix analysis, respectively. We find a significant tendency of ground motion in the gas emission area to be polarized in the horizontal plane, with a N115° predominant trend. This polarization tends to disappear while moving far from the site. According to previous papers in other study areas, such a directional effect is likely caused by fault-induced fractures and tends to be orthogonal to the fracture strike. The predominant NW–SE regional faulting does not fit the N115° polarization direction. To explain observations, we propose an interpretation in terms of a NE–SW oriented, local transfer fault as inferred from the lineament analysis. The intersection of the damage zone of this fault with the regional NW–SE normal fault system could easily be the responsible for the gas emissions since it favors a locally increased crustal weakness.     

A Comprehensive Method for Fractionating Soil Organic Matter Not Protected and Protected from Decomposition by Physical and Chemical Mechanisms

The objective of this work was to describe a method for isolating meaningful and measurable soil organic matter (SOM) pools that differ in the mechanisms by which they are protected from decomposition. The proposed method is appropriate for soil C stabilization and sequestration studies. Unlike previous fractionation schemes, this procedure allows free SOM located between aggregates (unprotected C pool) and SOM occluded within both macroaggregates and microaggregates (C weakly and strongly protected by physical mechanisms, respectively) to be recovered separately, freed from the soil mineral matrix and the mineral‐associated SOM pool (C pool protected by chemical mechanisms) and thus well suited to advanced chemical characterization by ¹³C‐NMR. Briefly, free SOM is isolated by an initial density separation. Stable macroaggregates are broken up into stable microaggregates and intra‐macroaggregate SOM, which is then separated by density. Finally, intra‐microaggregate SOM is isolated from mineral‐associated SOM by a third density separation after ultrasonic disruption. The SOM dissolved during the fractionation procedure is also recovered. Results obtained on soil samples with contrasting textures suggested that clay content induces a decrease of the proportion of free organic C and an increase of mineral‐associated organic C content. Free SOM is characterized by a marked presence of undecayed organic material and biologically labile substances, such as carbohydrates and proteins. In contrast, SOM occluded within aggregates, especially within microaggregates, represents a more decomposed fraction, relatively enriched in unsubstituted‐aliphatic material, most probably lipid biopolymers.     

青少年胫骨结节撕脱性骨折影像学诊断

目的:探讨急性青少年胫骨结节撕脱性骨折的影像学诊断价值。方法:回顾性分析经手术证实的6例(都为男性)急性青少年胫骨结节撕脱性骨折患者资料,其中2例右侧,4例左侧。除1例为跌倒致伤外,其余5例为运动损伤。X线平片检查6例,CT平扫2例,MRI平扫3例。结果:X线平片表现,根据Ogden’s分型,1例ⅠB型,1例ⅡA型、2例ⅡB型、1例ⅢA型、1例ⅢB型;6例均有髌骨上移征象。CT表现,2例ⅡB患者显示骨碎块移位,髌骨往上移位,其中1例合并髌骨陈旧性骨折。3例合并髌韧带撕裂,1例ⅡB型骨折合并髌韧带撕裂患者CT、MRI显示髌韧带肿胀,扭曲,T1WI、T2WI髌韧带信号增高。结论:X线平片是诊断急性胫骨结节撕脱性首选的影像方法,CT对骨折分型也有一定的帮助。怀疑有合并髌韧带、半月板等软组织损伤时,MRI具有重要诊断价值,对治疗方案的选择具有指导作用。     

Stream tube integration method for analysing subsurface fluid flow

A stream tube integration method is introduced to solve transient subsurface fluid flow problems. The method combines a geometry-embedded form of Darcy's Law and the notion of location of average. Two types of problems, transient radial flow to a well of finite radius in an areally infinite aquifer and in a double porosity system, are solved by the stream tube integration method and the integral finite difference method. Results of the solutions show that the stream tube integration method, with fixed coarse mesh, are more accurate and better behaved than the integral finite difference method, with fine mesh. The fixed mesh stream tube integration method is readily extended to the moving mesh method. With much coarse mesh, the moving mesh technique can obtain the same accurate results as the fixed mesh stream tube integration method. It is suggested that the stream tube integration method is a viable way to state, solve, interpret and verify numerical solutions. The method provides efficient computation and improved accuracy for analysing subsurface fluid flow. © 1998 John Wiley & Sons, Ltd.     

海啸波近岸共振响应的数值模拟及分析

应用有限差分方法求解非线性浅水长波方程,建立了海啸波产生和传播的二维数值模型;对太平洋地震引起的夏威夷群岛海啸波进行模拟,并将模拟结果和测站实测值进行比较,验证了模型的正确性。利用快速傅里叶变换对数值模拟结果进行谱分析,得到整个计算区域的能量谱分布,并给出了发生能量聚集的位置及相应的谱峰周期。讨论了海啸波传播到近岸时可能产生的共振响应现象,发现海啸波和近岸的共振响应不仅与近岸复杂地形有关,还与海啸波传播到近岸时的波浪入射方向有关。     

On the interest of using the multiple center approach in ESR dating of optically bleached quartz grains: Some examples from the Early Pleistocene terraces of the Alcanadre River (Ebro basin,Spain)

The present work reports the first numerical ages obtained for the two highest fluvial terraces (Qt1 and Qt2) of the Alcanadre River system (Northeastern Spain) representing the earliest remnants of Quaternary morphosedimentary fluvial activity in the Ebro basin. ESR dating method was applied to optically bleached quartz grains and both the Al and Ti centers were measured, in accordance with the Multiple Center approach. The results are overall in good agreement with the existing preliminary chronostratigraphic framework and our interpretation indicate that terraces Qt1 and Qt2 have an ESR age of 1276 ± 104 ka and 817 ± 68 ka, respectively. These data provide some chronological insights on the beginning of the fluvial sedimentary processes in a scenario of incision maintained over Quaternary in the Ebro Basin. These are among the first numerical ages obtained for such high terraces in the Iberian Peninsula.Our results demonstrate the interest of using the Multiple Center approach in ESR dating of quartz, since the two centers provide complementary information, i.e. an independent dose control. The overall apparent consistency between the ESR age estimates and the existing preliminary chronostratigraphic framework may be considered as an empirical evidence that the Ti–Li center may actually work for Early Pleistocene deposits, whereas the Ti–H center shows some clear limitations instead. Finally, these results demonstrate the interest of using ESR method to date Early Pleistocene fluvial terraces that are usually beyond the time range covered by the OSL dating method.     

水轮机流道压力脉动诱发厂房振动分析

水轮机压力脉动是引起厂房内源振动的主要诱因,如何在振动系统中合理、准确地施加水力荷载的振源特性,是目前机组振动分析的主要难点.文中将压力脉动假定为简谐荷载,通过跟踪楼板的振动变化和共振校核确定机组的振源特性,采用有限元法精细模拟了水轮机流道压力脉动诱发的厂房振动问题,并结合电站特点提出振动控制标准的建议值,由此对振动进...     

结构-地基体系水平与扭转位移耦合效应研究

采用动力理论对地基-结构非线性相互作用体系的振动方程进行了定性分析.基于多线性随动强化模型,采用非线性有限元法求解了基础和地基土之间的水平刚度与摇摆刚度,建立了结构-地基非线性相互作用体系的力学模型.利用拉格朗日能量法推导了结构水平位移和扭转相耦合的振动方程.采用多尺度法研究了结构-地基相互作用体系的主共振.通过分析不...     

应用核磁共振成像(NMRI)技术研究复合剂驱油特征

本文应用核磁共振成像技术,在均值、非均值模型中研究了复合剂驱油动态实验过程。观察及分析了复合剂驱油特征和效果,对复合剂驱油段塞前缘进行了实时跟踪,得到了复合剂驱油段塞前缘油墙的形成及剩余油分布与运移的二维图像,给出了复合剂驱油后,剩余油的饱和度分布曲线。实验表明:在层状非均值地层中,若渗透率差异大,复合剂段塞主要进入高渗层,而波及不到低渗层,即复合剂波及效率低。若渗透率差异小,复合剂段塞大部分进入高渗层,有少部分进入低渗层,即复合剂波及效率较高。